Recently, onium salts have been suggested as a solvent for dissolving cellulose (see, Patent Literature 1 and Non-Patent Literature 1, for example). In Patent Literature 1 describes a method of recycling cellulose by dissolving cellulose in an imidazolium-based onium salt such as 1-butyl-3-methylimidazolium chloride and mixing the obtained cellulose-containing onium salt with water. Non-Patent Literature 1 describes a method in which cellulose is dissolved in an imidazolium-based onium salt such as 1-ethyl-3-methylimidazolium acetate and 1-ethyl-3-methylimidazolium chloride, and a mixture of the obtained cellulose-containing ionic liquid added with dimethyl sulfoxide is mixed with methanol to precipitate the cellulose.
Accordingly, in view of Patent Literature 1 and Non-Patent Literature 1, inventors of the present invention tried dissolving cellulose by using an onium salt such as 1-ethyl-3-methylimidazolium chloride. However, when the onium salt described in Patent Literature 1 and Non-Patent Literature 1 is used, the solubility of cellulose was not fully satisfactory at 100° C. (see, Comparative Evaluation Examples that are described below).